Substrate assemblies typically include a substrate member having one or more patterned layers formed therein and thereon. A substrate member is often a semiconductor wafer, such as a slice of monocrystalline silicon. Layers may be grown, deposited, implanted, and in like ways formed.
As technology pushes forward, microlithography continues to resolve smaller and smaller images for patterning layers. Often it is necessary to create a an opening or "via" to access a feature below one or more layers of material. The ability to access such a feature may be severely limited by density of features in an area. So, even though sufficient area may be available for creating a via in an upper layer, such availability may not exist at or near a subsurface contact area. In particular, it would be desirable to provide access for an ohmic contact by virtue of creating a via for filling with an electrically conductive material.
One suggestion proposed by others for providing a via is to form a contact pedestal. In forming such a contact pedestal, the substrate assembly is etched to a first depth. After the etch step, a spacer layer is deposited over etched surfaces (including sidewalls). The spacer layer may be a polycrystalline silicon. The spacer layer is then anisotropically etched to form sidewall spacers within the contact opening. The contact opening is then etched again to increase the depth for via formation. The contact is then filled with an electrically conductive material, leaving the spacer in place.
It would, however, be desirable to provide a contact pedestal with fewer steps, and where the spacer was easily removed for substitution with a more conductive material.
In dry etching oxide, there are various chemistries which may be employed. Some chemistries cause a build-up of polymer. Specifically, in fluorocarbon oxide etch chemistries, a polymer by-product is generated during the etch process. Typically, this is a fluorocarbon polymer. Such fluorocarbon chemistries are known. However, in the past, it was difficult to obtain high anisotropy with fluorine chemistries for high aspect ratios and small critical dimensions.
Consequently, it would be desirable to provide better anisotropic control for small critical dimensions.